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[PATCH v6] README for 64bit xid
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* [PATCH v6] README for 64bit xid
@ 2022-01-10 19:20  Pavel Borisov <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Pavel Borisov @ 2022-01-10 19:20 UTC (permalink / raw)

Authors:
- Pavel Borisov <[email protected]>
- Maxim Orlov <[email protected]>
- Yura Sokolov <[email protected]> <[email protected]>
---
 src/backend/access/heap/README.XID64 | 128 +++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)
 create mode 100644 src/backend/access/heap/README.XID64

diff --git a/src/backend/access/heap/README.XID64 b/src/backend/access/heap/README.XID64
new file mode 100644
index 00000000000..457ba9b9ef5
--- /dev/null
+++ b/src/backend/access/heap/README.XID64
@@ -0,0 +1,128 @@
+src/backend/access/heap/README.XID64
+
+64-bit Transaction ID's (XID)
+=============================
+
+A limited number (N = 2^32) of XID's required to do vacuum freeze to prevent
+wraparound every N/2 transactions. This causes performance degradation due
+to the need to exclusively lock tables while being vacuumed. In each
+wraparound cycle, SLRU buffers are also being cut.
+
+With 64-bit XID's wraparound is effectively postponed to a very distant
+future. Even in highly loaded systems that had 2^32 transactions per day
+it will take huge 2^31 days before the first enforced "vacuum to prevent
+wraparound"). Buffers cutting and routine vacuum are not enforced, and DBA
+can plan them independently at the time with the least system load and least
+critical for database performance. Also, it can be done less frequently
+(several times a year vs every several days) on systems with transaction rates
+similar to those mentioned above.
+
+On-disk tuple and page format
+-----------------------------
+
+On-disk tuple format remains unchanged. 32-bit t_xmin and t_xmax store the
+lower parts of 64-bit XMIN and XMAX values. Each heap page has additional
+64-bit pd_xid_base and pd_multi_base which are common for all tuples on a page.
+They are placed into a pd_special area - 16 bytes in the end of a heap page.
+Actual XMIN/XMAX for a tuple are calculated upon reading a tuple from a page
+as follows:
+
+XMIN = t_xmin + pd_xid_base. 					(1)
+XMAX = t_xmax + pd_xid_base/pd_multi_base.		(2)
+
+"Double XMAX" page format
+---------------------------------
+
+At first read of a heap page after pg_upgrade from 32-bit XID PostgreSQL
+version pd_special area with a size of 16 bytes should be added to a page.
+Though a page may not have space for this. Then it can be converted to a
+temporary format called "double XMAX".
+
+All tuples after pg-upgrade would necessarily have xmin = FrozenTransactionId.
+So we don't need tuple header t_xmin field and we reuse t_xmin to store higher
+32 bits of its XMAX.
+
+Double XMAX format is only for full pages that don't have 16 bytes for
+pd_special. So it neither has a�place for a single tuple. Insert and HOT update
+for double XMAX pages is impossible and not supported. We can only read or
+delete tuples from it.
+
+When we are able to prune page double XMAX it will be converted from it to
+general 64-bit XID page format with all operations on its tuples supported.
+
+In-memory tuple format
+----------------------
+
+In-memory tuple representation consists of two parts:
+- HeapTupleHeader from disk page (contains all heap tuple contents, not only
+header)
+- HeapTuple with additional in-memory fields
+
+HeapTuple for each tuple in memory stores t_xid_base/t_multi_base - a copies of
+page's pd_xid_base/pd_multi_base. With tuple's 32-bit t_xmin and t_xmax from
+HeapTupleHeader they are used to calculate actual 64-bit XMIN and XMAX:
+
+XMIN = t_xmin + t_xid_base. 					(3)
+XMAX = t_xmax + t_xid_base/t_multi_base.		(4)
+
+The downside of this is that we can not use tuple's XMIN and XMAX right away.
+We often need to re-read t_xmin and t_xmax - which could actually be pointers
+into a page in shared buffers and therefore they could be updated by any other
+backend.
+
+Update/delete with 64-bit XIDs and 32-bit t_xmin/t_xmax
+--------------------------------------------------------------
+
+When we try to delete/update a tuple, we check that XMAX for a page fits (2).
+I.e. that t_xmax will not be over MaxShortTransactionId relative to
+pd_xid_base/pd_multi_base of a its page.
+
+If the current XID doesn't fit a range
+(pd_xid_base, pd_xid_base + MaxShortTransactionId) (5):
+
+- heap_page_prepare_for_xid() will try to increase pd_xid_base/pd_multi_base on
+a page and update all t_xmin/t_xmax of the other tuples on the page to
+correspond new pd_xid_base/pd_multi_base.
+
+- If it was impossible, it will try to prune and freeze tuples on a page.
+
+- If this is unsuccessful it will throw an error. Normally this is very
+unlikely but if there is a very old living transaction with an age of around
+2^32 this can arise. Basically, this is a behavior similar to one during the
+vacuum to prevent wraparound when XID was 32-bit. Dba should take care and
+avoid very-long-living transactions with an age close to 2^32. So long-living
+transactions often they are most likely defunct.
+
+Insert with 64-bit XIDs and 32-bit t_xmin/t_xmax
+------------------------------------------------
+
+On insert we check if current XID fits a range (5). Otherwise:
+
+- heap_page_prepare_for_xid() will try to increase pd_xid_base for t_xmin will
+not be over MaxShortTransactionId.
+
+- If it is impossible, then it will try to prune and freeze tuples on a page.
+
+Known issue: if pd_xid_base could not be shifted to accommodate a tuple being
+inserted due to a very long-running transaction, we just throw an error. We
+neither try to insert a�tuple into another page nor mark the current page as
+full. So, in this (unlikely) case we will get regular insert errors on the next
+tries to insert to the page 'locked' by this very long-running transaction.
+
+Upgrade from 32-bit XID versions
+--------------------------------
+
+pg_upgrade doesn't change pages format itself. It is done lazily after.
+
+1. At first heap page read, tuples on a page are repacked to free 16 bytes
+at the end of a page, possibly freeing space from dead tuples.
+
+2A. 16 bytes of pd_special is added if there is a place for it
+
+2B. Page is converted to "Double XMAX" format if there is no place for
+pd_special
+
+3. If a page is in double XMAX format after its first read, and vacuum (or
+micro-vacuum at select query) could prune some tuples and free space for
+pd_special, prune_page will add pd_special and convert page from double XMAX
+to general 64-bit XID page format.
-- 
2.24.3 (Apple Git-128)


--cpok4wp6gsarlzvp--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v1] solaris: Use versioning scripts instead of -Bsymbolic
@ 2022-08-23 08:50  Andres Freund <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Andres Freund @ 2022-08-23 08:50 UTC (permalink / raw)

-Bsymbolic causes a lot of "ld: warning: symbol referencing errors"
warnings. It's quite easy to add the symbol versioning script, we just need a
slightly different parameter name.

Discussion: https://postgr.es/m/[email protected]
---
 src/Makefile.shlib | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/Makefile.shlib b/src/Makefile.shlib
index 2af6192f0f3..3202b2e67de 100644
--- a/src/Makefile.shlib
+++ b/src/Makefile.shlib
@@ -188,10 +188,15 @@ ifeq ($(PORTNAME), linux)
 endif
 
 ifeq ($(PORTNAME), solaris)
-  LINK.shared		= $(COMPILER) -shared -Wl,-Bsymbolic
+  LINK.shared		= $(COMPILER) -shared
   ifdef soname
     LINK.shared	+= -Wl,-soname,$(soname)
   endif
+  BUILD.exports		= ( echo '{ global:'; $(AWK) '/^[^\#]/ {printf "%s;\n",$$1}' $<; echo ' local: *; };' ) >$@
+  exports_file		= $(SHLIB_EXPORTS:%.txt=%.list)
+  ifneq (,$(exports_file))
+    LINK.shared		+= -Wl,-M$(exports_file)
+  endif
 endif
 
 ifeq ($(PORTNAME), cygwin)
-- 
2.37.0.3.g30cc8d0f14


--aym2ahtpoerge4dw--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v44 10/10] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 140 insertions(+), 23 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 018e9f7b013..423cea26b0b 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1075,6 +1075,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..b02ec4e8c3e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..c785a3db59f 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1370,9 +1373,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 1dad125706e..c6693b93a65 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -69,10 +69,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--gwom7bl7ogtszo4k--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v45 8/8] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 7291b4180ab..0103bc10bd1 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--cldir6umqisr673d--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v46 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 21ab81c6f7f..42165c5552e 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--mdsv5bdgfjjj6d77--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v47 9/9] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 3acb2e1d2ba..74faa4f5582 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--2fxmamo6mu2qbxgv--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v48 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 51 +++++++++-----
 src/backend/storage/ipc/procarray.c         | 75 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  2 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 144 insertions(+), 27 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..58ebecf4927 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId *xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 781a471fc1d..29ba49744eb 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is o.k.
+		 * for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..f2008c6877c 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
-	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
-	 * means all transactions starting afterwards have enough information to
-	 * be decoded.  Switch to FULL_SNAPSHOT.
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * BUILDING_SNAPSHOT.  This means all transactions starting afterwards
+	 * have enough information to be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,15 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
-	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
-	 * transactions that are currently in progress have a catalog snapshot,
-	 * and all their changes have been collected.  Switch to CONSISTENT.
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * FULL_SNAPSHOT.  This means all transactions that are currently in
+	 * progress have a catalog snapshot, and all their changes have been
+	 * collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1460,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId *xids_repack;
+			int			i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..033ae68b57e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,25 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count,
+				count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId *xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2673,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int			nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2689,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2704,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2713,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2734,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2756,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2775,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2828,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2850,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..fe4dcdc3def 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,12 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--qfkt2ktdpcfeypib--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v49 6/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 51 +++++++++-----
 src/backend/storage/ipc/procarray.c         | 75 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  2 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 144 insertions(+), 27 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..58ebecf4927 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId *xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 274ad900c65..5188244dfd6 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -993,6 +993,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is o.k.
+		 * for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 0f6b5df322c..23511a0905a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
-	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
-	 * means all transactions starting afterwards have enough information to
-	 * be decoded.  Switch to FULL_SNAPSHOT.
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * BUILDING_SNAPSHOT.  This means all transactions starting afterwards
+	 * have enough information to be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,15 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
-	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
-	 * transactions that are currently in progress have a catalog snapshot,
-	 * and all their changes have been collected.  Switch to CONSISTENT.
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * FULL_SNAPSHOT.  This means all transactions that are currently in
+	 * progress have a catalog snapshot, and all their changes have been
+	 * collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1460,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId *xids_repack;
+			int			i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..033ae68b57e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,25 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count,
+				count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId *xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2673,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int			nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2689,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2704,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2713,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2734,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2756,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2775,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2828,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2850,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..fe4dcdc3def 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,12 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--3n3vqr5y2jhknrqj
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v49-0007-WIP-add-max_repack_replication_slots.patch"



^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 73 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  6 +-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 138 insertions(+), 22 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..79c052d3607 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXid %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 4fd10a5e7b3..73407c383da 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1086,6 +1086,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 0f913897acc..f1a03e6a754 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,13 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2687,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2702,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2711,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2732,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2754,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2773,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2826,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2848,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..5c4121fcbc8 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1372,7 +1375,8 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	/* array of TransactionIds */
 	if (xlrec.xcnt > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index bf3094f0f7d..120370f459d 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -67,10 +67,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index c63a4f2cc6a..0bd28e270f1 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -124,10 +124,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--=-=-=--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v43 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 73 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  6 +-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 138 insertions(+), 22 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..79c052d3607 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXid %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 065316ee866..77c206ff944 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1084,6 +1084,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 0f913897acc..f1a03e6a754 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,13 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2687,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2702,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2711,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2732,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2754,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2773,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2826,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2848,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..5c4121fcbc8 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1372,7 +1375,8 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	/* array of TransactionIds */
 	if (xlrec.xcnt > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index bf3094f0f7d..120370f459d 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -67,10 +67,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index c63a4f2cc6a..0bd28e270f1 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -124,10 +124,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--nzintiedl6o4kcyp--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v44 10/10] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 140 insertions(+), 23 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 018e9f7b013..423cea26b0b 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1075,6 +1075,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..b02ec4e8c3e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..c785a3db59f 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1370,9 +1373,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 1dad125706e..c6693b93a65 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -69,10 +69,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--gwom7bl7ogtszo4k--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v45 8/8] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 7291b4180ab..0103bc10bd1 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--cldir6umqisr673d--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v46 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 21ab81c6f7f..42165c5552e 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--mdsv5bdgfjjj6d77--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v47 9/9] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 3acb2e1d2ba..74faa4f5582 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--2fxmamo6mu2qbxgv--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v48 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 51 +++++++++-----
 src/backend/storage/ipc/procarray.c         | 75 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  2 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 144 insertions(+), 27 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..58ebecf4927 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId *xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 781a471fc1d..29ba49744eb 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is o.k.
+		 * for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..f2008c6877c 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
-	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
-	 * means all transactions starting afterwards have enough information to
-	 * be decoded.  Switch to FULL_SNAPSHOT.
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * BUILDING_SNAPSHOT.  This means all transactions starting afterwards
+	 * have enough information to be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,15 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
-	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
-	 * transactions that are currently in progress have a catalog snapshot,
-	 * and all their changes have been collected.  Switch to CONSISTENT.
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * FULL_SNAPSHOT.  This means all transactions that are currently in
+	 * progress have a catalog snapshot, and all their changes have been
+	 * collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1460,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId *xids_repack;
+			int			i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..033ae68b57e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,25 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count,
+				count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId *xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2673,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int			nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2689,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2704,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2713,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2734,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2756,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2775,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2828,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2850,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..fe4dcdc3def 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,12 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--qfkt2ktdpcfeypib--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v49 6/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 51 +++++++++-----
 src/backend/storage/ipc/procarray.c         | 75 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  2 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 144 insertions(+), 27 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..58ebecf4927 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId *xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 274ad900c65..5188244dfd6 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -993,6 +993,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is o.k.
+		 * for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 0f6b5df322c..23511a0905a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
-	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
-	 * means all transactions starting afterwards have enough information to
-	 * be decoded.  Switch to FULL_SNAPSHOT.
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * BUILDING_SNAPSHOT.  This means all transactions starting afterwards
+	 * have enough information to be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,15 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
-	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
-	 * transactions that are currently in progress have a catalog snapshot,
-	 * and all their changes have been collected.  Switch to CONSISTENT.
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * FULL_SNAPSHOT.  This means all transactions that are currently in
+	 * progress have a catalog snapshot, and all their changes have been
+	 * collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1460,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId *xids_repack;
+			int			i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..033ae68b57e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,25 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count,
+				count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId *xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2673,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int			nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2689,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2704,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2713,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2734,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2756,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2775,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2828,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2850,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..fe4dcdc3def 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,12 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--3n3vqr5y2jhknrqj
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v49-0007-WIP-add-max_repack_replication_slots.patch"



^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 73 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  6 +-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 138 insertions(+), 22 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..79c052d3607 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXid %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 4fd10a5e7b3..73407c383da 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1086,6 +1086,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 0f913897acc..f1a03e6a754 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,13 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2687,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2702,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2711,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2732,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2754,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2773,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2826,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2848,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..5c4121fcbc8 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1372,7 +1375,8 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	/* array of TransactionIds */
 	if (xlrec.xcnt > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index bf3094f0f7d..120370f459d 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -67,10 +67,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index c63a4f2cc6a..0bd28e270f1 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -124,10 +124,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--=-=-=--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v43 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 73 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  6 +-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 138 insertions(+), 22 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..79c052d3607 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXid %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 065316ee866..77c206ff944 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1084,6 +1084,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 0f913897acc..f1a03e6a754 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,13 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2687,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2702,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2711,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2732,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2754,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2773,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2826,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2848,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..5c4121fcbc8 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1372,7 +1375,8 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	/* array of TransactionIds */
 	if (xlrec.xcnt > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index bf3094f0f7d..120370f459d 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -67,10 +67,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index c63a4f2cc6a..0bd28e270f1 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -124,10 +124,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--nzintiedl6o4kcyp--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v44 10/10] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 140 insertions(+), 23 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 018e9f7b013..423cea26b0b 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1075,6 +1075,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..b02ec4e8c3e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..c785a3db59f 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1370,9 +1373,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 1dad125706e..c6693b93a65 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -69,10 +69,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--gwom7bl7ogtszo4k--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v45 8/8] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 7291b4180ab..0103bc10bd1 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--cldir6umqisr673d--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v46 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 21ab81c6f7f..42165c5552e 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--mdsv5bdgfjjj6d77--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v47 9/9] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 3acb2e1d2ba..74faa4f5582 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--2fxmamo6mu2qbxgv--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v48 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 51 +++++++++-----
 src/backend/storage/ipc/procarray.c         | 75 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  2 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 144 insertions(+), 27 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..58ebecf4927 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId *xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 781a471fc1d..29ba49744eb 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is o.k.
+		 * for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..f2008c6877c 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
-	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
-	 * means all transactions starting afterwards have enough information to
-	 * be decoded.  Switch to FULL_SNAPSHOT.
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * BUILDING_SNAPSHOT.  This means all transactions starting afterwards
+	 * have enough information to be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,15 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
-	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
-	 * transactions that are currently in progress have a catalog snapshot,
-	 * and all their changes have been collected.  Switch to CONSISTENT.
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * FULL_SNAPSHOT.  This means all transactions that are currently in
+	 * progress have a catalog snapshot, and all their changes have been
+	 * collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1460,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId *xids_repack;
+			int			i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..033ae68b57e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,25 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count,
+				count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId *xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2673,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int			nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2689,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2704,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2713,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2734,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2756,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2775,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2828,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2850,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..fe4dcdc3def 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,12 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--qfkt2ktdpcfeypib--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v49 6/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 51 +++++++++-----
 src/backend/storage/ipc/procarray.c         | 75 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  2 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 144 insertions(+), 27 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..58ebecf4927 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId *xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 274ad900c65..5188244dfd6 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -993,6 +993,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is o.k.
+		 * for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 0f6b5df322c..23511a0905a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
-	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
-	 * means all transactions starting afterwards have enough information to
-	 * be decoded.  Switch to FULL_SNAPSHOT.
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * BUILDING_SNAPSHOT.  This means all transactions starting afterwards
+	 * have enough information to be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,15 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
-	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
-	 * transactions that are currently in progress have a catalog snapshot,
-	 * and all their changes have been collected.  Switch to CONSISTENT.
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * FULL_SNAPSHOT.  This means all transactions that are currently in
+	 * progress have a catalog snapshot, and all their changes have been
+	 * collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1460,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId *xids_repack;
+			int			i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..033ae68b57e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,25 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count,
+				count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId *xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2673,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int			nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2689,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2704,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2713,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2734,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2756,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2775,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2828,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2850,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..fe4dcdc3def 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,12 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--3n3vqr5y2jhknrqj
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v49-0007-WIP-add-max_repack_replication_slots.patch"



^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 73 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  6 +-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 138 insertions(+), 22 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..79c052d3607 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXid %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 4fd10a5e7b3..73407c383da 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1086,6 +1086,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 0f913897acc..f1a03e6a754 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,13 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2687,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2702,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2711,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2732,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2754,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2773,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2826,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2848,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..5c4121fcbc8 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1372,7 +1375,8 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	/* array of TransactionIds */
 	if (xlrec.xcnt > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index bf3094f0f7d..120370f459d 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -67,10 +67,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index c63a4f2cc6a..0bd28e270f1 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -124,10 +124,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--=-=-=--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v43 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 73 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  6 +-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 138 insertions(+), 22 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..79c052d3607 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXid %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 065316ee866..77c206ff944 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1084,6 +1084,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 0f913897acc..f1a03e6a754 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,13 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2687,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2702,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2711,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2732,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2754,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2773,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2826,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2848,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..5c4121fcbc8 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1372,7 +1375,8 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	/* array of TransactionIds */
 	if (xlrec.xcnt > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index bf3094f0f7d..120370f459d 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -67,10 +67,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index c63a4f2cc6a..0bd28e270f1 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -124,10 +124,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--nzintiedl6o4kcyp--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v44 10/10] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 140 insertions(+), 23 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 018e9f7b013..423cea26b0b 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1075,6 +1075,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..b02ec4e8c3e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..c785a3db59f 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1370,9 +1373,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 1dad125706e..c6693b93a65 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -69,10 +69,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--gwom7bl7ogtszo4k--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v45 8/8] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 7291b4180ab..0103bc10bd1 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--cldir6umqisr673d--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v46 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 21ab81c6f7f..42165c5552e 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--mdsv5bdgfjjj6d77--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v47 9/9] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 137 insertions(+), 21 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 3acb2e1d2ba..74faa4f5582 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..6dd4fa7dcc0 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--2fxmamo6mu2qbxgv--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v48 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 51 +++++++++-----
 src/backend/storage/ipc/procarray.c         | 75 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  2 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 144 insertions(+), 27 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..58ebecf4927 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId *xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 781a471fc1d..29ba49744eb 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -988,6 +988,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is o.k.
+		 * for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..f2008c6877c 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
-	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
-	 * means all transactions starting afterwards have enough information to
-	 * be decoded.  Switch to FULL_SNAPSHOT.
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * BUILDING_SNAPSHOT.  This means all transactions starting afterwards
+	 * have enough information to be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,15 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
-	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
-	 * transactions that are currently in progress have a catalog snapshot,
-	 * and all their changes have been collected.  Switch to CONSISTENT.
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * FULL_SNAPSHOT.  This means all transactions that are currently in
+	 * progress have a catalog snapshot, and all their changes have been
+	 * collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1460,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId *xids_repack;
+			int			i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..033ae68b57e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,25 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count,
+				count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId *xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2673,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int			nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2689,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2704,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2713,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2734,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2756,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2775,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2828,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2850,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..fe4dcdc3def 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,12 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--qfkt2ktdpcfeypib--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v49 6/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/repack.c               | 16 +++++
 src/backend/replication/logical/snapbuild.c | 51 +++++++++-----
 src/backend/storage/ipc/procarray.c         | 75 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/storage/standby.h               |  2 +
 src/include/storage/standbydefs.h           |  2 +
 8 files changed, 144 insertions(+), 27 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..58ebecf4927 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId *xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2c1c6f88b74..f1cbdee7618 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8483,6 +8484,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 274ad900c65..5188244dfd6 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -993,6 +993,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is o.k.
+		 * for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 0f6b5df322c..23511a0905a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
-	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
-	 * means all transactions starting afterwards have enough information to
-	 * be decoded.  Switch to FULL_SNAPSHOT.
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * BUILDING_SNAPSHOT.  This means all transactions starting afterwards
+	 * have enough information to be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,15 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
-	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
-	 * transactions that are currently in progress have a catalog snapshot,
-	 * and all their changes have been collected.  Switch to CONSISTENT.
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts'
+	 * oldestRunningXidLogical is >= than nextXid from when we switched to
+	 * FULL_SNAPSHOT.  This means all transactions that are currently in
+	 * progress have a catalog snapshot, and all their changes have been
+	 * collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1460,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId *xids_repack;
+			int			i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..033ae68b57e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,25 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count,
+				count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId *xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2673,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int			nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2689,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2704,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2713,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2734,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_CONCURRENT_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2756,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2775,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2828,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2850,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..fd3e4fe31f3 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1189,6 +1189,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1359,10 +1360,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1371,9 +1374,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..fe4dcdc3def 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,12 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--3n3vqr5y2jhknrqj
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v49-0007-WIP-add-max_repack_replication_slots.patch"



^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 73 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  6 +-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 138 insertions(+), 22 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..79c052d3607 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXid %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 4fd10a5e7b3..73407c383da 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1086,6 +1086,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 0f913897acc..f1a03e6a754 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,13 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2687,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2702,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2711,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2732,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2754,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2773,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2826,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2848,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..5c4121fcbc8 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1372,7 +1375,8 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	/* array of TransactionIds */
 	if (xlrec.xcnt > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index bf3094f0f7d..120370f459d 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -67,10 +67,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index c63a4f2cc6a..0bd28e270f1 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -124,10 +124,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--=-=-=--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v43 7/7] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 73 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  6 +-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 138 insertions(+), 22 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..79c052d3607 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXid %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 065316ee866..77c206ff944 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1084,6 +1084,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 0f913897acc..f1a03e6a754 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,13 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2687,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2702,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2711,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2732,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2754,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2773,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2826,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2848,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..5c4121fcbc8 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1372,7 +1375,8 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	/* array of TransactionIds */
 	if (xlrec.xcnt > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index bf3094f0f7d..120370f459d 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -67,10 +67,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index c63a4f2cc6a..0bd28e270f1 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -124,10 +124,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--nzintiedl6o4kcyp--





^ permalink  raw  reply  [nested|flat] 802+ messages in thread

* [PATCH v44 10/10] Teach snapshot builder to skip transactions running REPACK (CONCURRENTLY).
@ 2026-03-17 19:22  Antonin Houska <[email protected]>
  0 siblings, 0 replies; 802+ messages in thread

From: Antonin Houska @ 2026-03-17 19:22 UTC (permalink / raw)

During logical decoding, we need to know if particular transaction performed
catalog changes because catalog information is needed to construct heap
tuples. To be sure that we have enough information of each transaction, the
logical decoding cannot start before all the already running transactions have
completed.

The problem with REPACK (CONCURRENTLY) is that it has XID assigned and writes
WAL records marked with it. Thus if another backend runs REPACK (CONCURRENTLY)
and tries to setup the logical decoding, it has to wait for the completion of
all the other transactions involved in REPACK (CONCURRENTLY).

However, REPACK (CONCURRENTLY) does not perform any catalog changes relevant
to logical decoding, so the other backends executing this command can ignore
it. This patch implements it by adding information about transactions
executing the command to the xl_running_xacts WAL record, and by teaching the
snapshot builder to use the information.
---
 src/backend/access/rmgrdesc/standbydesc.c   | 15 ++++-
 src/backend/access/transam/xlog.c           |  2 +
 src/backend/commands/cluster.c              | 16 +++++
 src/backend/replication/logical/snapbuild.c | 38 ++++++++---
 src/backend/storage/ipc/procarray.c         | 74 +++++++++++++++++++--
 src/backend/storage/ipc/standby.c           |  8 ++-
 src/include/access/xlog_internal.h          |  2 +-
 src/include/storage/proc.h                  |  3 +-
 src/include/storage/standby.h               |  3 +
 src/include/storage/standbydefs.h           |  2 +
 10 files changed, 140 insertions(+), 23 deletions(-)

diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..b96b73d51d3 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -21,10 +21,11 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 {
 	int			i;
 
-	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u",
+	appendStringInfo(buf, "nextXid %u latestCompletedXid %u oldestRunningXid %u oldestRunningXidLogical %u",
 					 xlrec->nextXid,
 					 xlrec->latestCompletedXid,
-					 xlrec->oldestRunningXid);
+					 xlrec->oldestRunningXid,
+					 xlrec->oldestRunningXidLogical);
 	if (xlrec->xcnt > 0)
 	{
 		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
@@ -41,6 +42,16 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
 		for (i = 0; i < xlrec->subxcnt; i++)
 			appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
 	}
+
+	if (xlrec->xcnt_repack > 0)
+	{
+		TransactionId	*xids_repack;
+
+		appendStringInfo(buf, "; %d xacts_repack:", xlrec->xcnt_repack);
+		xids_repack = xlrec->xids + xlrec->xcnt + xlrec->subxcnt;
+		for (i = 0; i < xlrec->xcnt_repack; i++)
+			appendStringInfo(buf, " %u", xids_repack[i]);
+	}
 }
 
 void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f5c9a34374d..d050b0b1444 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5912,6 +5912,7 @@ StartupXLOG(void)
 				 * subxids are listed with their parent prepared transactions.
 				 */
 				running.xcnt = nxids;
+				running.xcnt_repack = 0;
 				running.subxcnt = 0;
 				running.subxid_status = SUBXIDS_IN_SUBTRANS;
 				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
@@ -8477,6 +8478,7 @@ xlog_redo(XLogReaderState *record)
 			 * with their parent prepared transactions.
 			 */
 			running.xcnt = nxids;
+			running.xcnt_repack = 0;
 			running.subxcnt = 0;
 			running.subxid_status = SUBXIDS_IN_SUBTRANS;
 			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 018e9f7b013..423cea26b0b 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -1075,6 +1075,22 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 
 	if (concurrent)
 	{
+		/*
+		 * Do not let other backends wait for our completion during their
+		 * setup of logical replication. Unlike logical replication publisher,
+		 * we will have XID assigned, so the other backends - whether
+		 * walsenders involved in logical replication or regular backends
+		 * executing also REPACK (CONCURRENTLY) - would have to wait for our
+		 * completion before they can build their initial snapshot. It is
+		 * o.k. for any decoding backend to ignore us because we do not change
+		 * tuple descriptor of any table, and the data changes we write should
+		 * not be decoded by other backends.
+		 */
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+		MyProc->statusFlags |= PROC_IN_REPACK;
+		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
+		LWLockRelease(ProcArrayLock);
+
 		/*
 		 * The worker needs to be member of the locking group we're the leader
 		 * of. We ought to become the leader before the worker starts. The
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 9cf499ce7c6..fbdd4600a2b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1172,7 +1172,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 * xmin, which looks odd but is correct and actually more efficient, since
 	 * we hit fast paths in heapam_visibility.c.
 	 */
-	builder->xmin = running->oldestRunningXid;
+	builder->xmin = running->oldestRunningXidLogical;
 
 	/* Remove transactions we don't need to keep track off anymore */
 	SnapBuildPurgeOlderTxn(builder);
@@ -1188,9 +1188,9 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
 	 */
 	xmin = ReorderBufferGetOldestXmin(builder->reorder);
 	if (xmin == InvalidTransactionId)
-		xmin = running->oldestRunningXid;
+		xmin = running->oldestRunningXidLogical;
 	elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
-		 builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
+		 builder->xmin, builder->xmax, running->oldestRunningXidLogical, xmin);
 	LogicalIncreaseXminForSlot(lsn, xmin);
 
 	/*
@@ -1275,14 +1275,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * have all necessary catalog rows anymore.
 	 */
 	if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
-		NormalTransactionIdPrecedes(running->oldestRunningXid,
+		NormalTransactionIdPrecedes(running->oldestRunningXidLogical,
 									builder->initial_xmin_horizon))
 	{
 		ereport(DEBUG1,
 				errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
 								LSN_FORMAT_ARGS(lsn)),
 				errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
-								   builder->initial_xmin_horizon, running->oldestRunningXid));
+								   builder->initial_xmin_horizon, running->oldestRunningXidLogical));
 
 
 		SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
@@ -1299,7 +1299,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	 * NB: We might have already started to incrementally assemble a snapshot,
 	 * so we need to be careful to deal with that.
 	 */
-	if (running->oldestRunningXid == running->nextXid)
+	if (running->oldestRunningXidLogical == running->nextXid)
 	{
 		if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
 			builder->start_decoding_at <= lsn)
@@ -1378,14 +1378,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
 	 *
-	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
+	 * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical
 	 * is >= than nextXid from when we switched to BUILDING_SNAPSHOT.  This
 	 * means all transactions starting afterwards have enough information to
 	 * be decoded.  Switch to FULL_SNAPSHOT.
 	 */
 	else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_FULL_SNAPSHOT;
 		builder->next_phase_at = running->nextXid;
@@ -1402,14 +1402,14 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
 	/*
 	 * c) transition from FULL_SNAPSHOT to CONSISTENT.
 	 *
-	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
+	 * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXidLogical is
 	 * >= than nextXid from when we switched to FULL_SNAPSHOT.  This means all
 	 * transactions that are currently in progress have a catalog snapshot,
 	 * and all their changes have been collected.  Switch to CONSISTENT.
 	 */
 	else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
 			 TransactionIdPrecedesOrEquals(builder->next_phase_at,
-										   running->oldestRunningXid))
+										   running->oldestRunningXidLogical))
 	{
 		builder->state = SNAPBUILD_CONSISTENT;
 		builder->next_phase_at = InvalidTransactionId;
@@ -1459,6 +1459,24 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
 		if (TransactionIdFollows(xid, cutoff))
 			continue;
 
+		/* Do not wait for transactions running REPACK (CONCURRENTLY). */
+		if (running->xcnt_repack > 0)
+		{
+			TransactionId	*xids_repack;
+			int		i;
+
+			xids_repack = running->xids + running->xcnt + running->subxcnt;
+
+			for (i = 0; i < running->xcnt_repack; i++)
+			{
+				if (xid == xids_repack[i])
+					break;
+			}
+			/* Found? */
+			if (i < running->xcnt_repack)
+				continue;
+		}
+
 		XactLockTableWait(xid, NULL, NULL, XLTW_None);
 	}
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index cc207cb56e3..b02ec4e8c3e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2643,15 +2643,24 @@ GetRunningTransactionData(void)
 	RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
 	TransactionId latestCompletedXid;
 	TransactionId oldestRunningXid;
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid;
 	TransactionId *xids;
 	int			index;
-	int			count;
+	int			count, count_repack;
 	int			subcount;
 	bool		suboverflowed;
+	TransactionId	*xids_repack = NULL;
+	bool		logical_decoding_enabled = IsLogicalDecodingEnabled();
 
 	Assert(!RecoveryInProgress());
 
+	/*
+	 * TODO Consider a GUC to reserve certain amount of replication slots for
+	 * REPACK (CONCURRENTLY) and using it here.
+	 */
+#define		MAX_REPACK_XIDS		16
+
 	/*
 	 * Allocating space for maxProcs xids is usually overkill; numProcs would
 	 * be sufficient.  But it seems better to do the malloc while not holding
@@ -2663,11 +2672,14 @@ GetRunningTransactionData(void)
 	 */
 	if (CurrentRunningXacts->xids == NULL)
 	{
+		/* FIXME probably fails if logical decoding is enable on-the-fly */
+		int		nrepack = logical_decoding_enabled ? MAX_REPACK_XIDS : 0;
+
 		/*
 		 * First call
 		 */
 		CurrentRunningXacts->xids = (TransactionId *)
-			malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
+			malloc((TOTAL_MAX_CACHED_SUBXIDS + nrepack) * sizeof(TransactionId));
 		if (CurrentRunningXacts->xids == NULL)
 			ereport(ERROR,
 					(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -2676,7 +2688,10 @@ GetRunningTransactionData(void)
 
 	xids = CurrentRunningXacts->xids;
 
-	count = subcount = 0;
+	if (logical_decoding_enabled)
+		xids_repack = palloc_array(TransactionId, MAX_REPACK_XIDS);
+
+	count = subcount = count_repack = 0;
 	suboverflowed = false;
 
 	/*
@@ -2688,7 +2703,7 @@ GetRunningTransactionData(void)
 
 	latestCompletedXid =
 		XidFromFullTransactionId(TransamVariables->latestCompletedXid);
-	oldestDatabaseRunningXid = oldestRunningXid =
+	oldestDatabaseRunningXid = oldestRunningXid = oldestRunningXidLogical =
 		XidFromFullTransactionId(TransamVariables->nextXid);
 
 	/*
@@ -2697,6 +2712,8 @@ GetRunningTransactionData(void)
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
 		TransactionId xid;
+		int			pgprocno;
+		PGPROC	   *proc;
 
 		/* Fetch xid just once - see GetNewTransactionId */
 		xid = UINT32_ACCESS_ONCE(other_xids[index]);
@@ -2716,6 +2733,21 @@ GetRunningTransactionData(void)
 		if (TransactionIdPrecedes(xid, oldestRunningXid))
 			oldestRunningXid = xid;
 
+		if (logical_decoding_enabled &&
+			TransactionIdPrecedes(xid, oldestRunningXidLogical))
+		{
+			/*
+			 * Backends running REPACK concurrently need to be excluded from
+			 * oldestRunningXidLogical, otherwise the snapshot builder cannot
+			 * proceed in building the initial snapshot.
+			 */
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if ((proc->statusFlags & PROC_IN_REPACK) == 0)
+				oldestRunningXidLogical = xid;
+		}
+
 		/*
 		 * Also, update the oldest running xid within the current database. As
 		 * fetching pgprocno and PGPROC could cause cache misses, we do cheap
@@ -2723,8 +2755,8 @@ GetRunningTransactionData(void)
 		 */
 		if (TransactionIdPrecedes(xid, oldestDatabaseRunningXid))
 		{
-			int			pgprocno = arrayP->pgprocnos[index];
-			PGPROC	   *proc = &allProcs[pgprocno];
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
 
 			if (proc->databaseId == MyDatabaseId)
 				oldestDatabaseRunningXid = xid;
@@ -2742,6 +2774,19 @@ GetRunningTransactionData(void)
 		 */
 
 		xids[count++] = xid;
+
+		/*
+		 * Collect XIDSs of transactions running REPACK (CONCURRENTLY).
+		 */
+		if (logical_decoding_enabled &&
+			count_repack < MAX_REPACK_XIDS)
+		{
+			pgprocno = arrayP->pgprocnos[index];
+			proc = &allProcs[pgprocno];
+
+			if (proc->statusFlags & PROC_IN_REPACK)
+				xids_repack[count_repack++] = xid;
+		}
 	}
 
 	/*
@@ -2782,6 +2827,19 @@ GetRunningTransactionData(void)
 		}
 	}
 
+	/*
+	 * Append the XIDs running REPACK (CONCURRENTLY), if any.
+	 *
+	 * XXX Should we sort the array and use bsearch() when using it?
+	 */
+	if (count_repack > 0)
+	{
+		for (int i = 0; i < count_repack; i++)
+			xids[count++] = xids_repack[i];
+	}
+	if (xids_repack)
+		pfree(xids_repack);
+
 	/*
 	 * It's important *not* to include the limits set by slots here because
 	 * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
@@ -2791,11 +2849,13 @@ GetRunningTransactionData(void)
 	 * increases if slots do.
 	 */
 
-	CurrentRunningXacts->xcnt = count - subcount;
+	CurrentRunningXacts->xcnt = count - subcount - count_repack;
 	CurrentRunningXacts->subxcnt = subcount;
+	CurrentRunningXacts->xcnt_repack = count_repack;
 	CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
 	CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
 	CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
+	CurrentRunningXacts->oldestRunningXidLogical = oldestRunningXidLogical;
 	CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
 	CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
 
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index f3ad90c7c7a..c785a3db59f 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,7 @@ standby_redo(XLogReaderState *record)
 		RunningTransactionsData running;
 
 		running.xcnt = xlrec->xcnt;
+		running.xcnt_repack = xlrec->xcnt_repack;
 		running.subxcnt = xlrec->subxcnt;
 		running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
 		running.nextXid = xlrec->nextXid;
@@ -1358,10 +1359,12 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRecPtr	recptr;
 
 	xlrec.xcnt = CurrRunningXacts->xcnt;
+	xlrec.xcnt_repack = CurrRunningXacts->xcnt_repack;
 	xlrec.subxcnt = CurrRunningXacts->subxcnt;
 	xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
 	xlrec.nextXid = CurrRunningXacts->nextXid;
 	xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
+	xlrec.oldestRunningXidLogical = CurrRunningXacts->oldestRunningXidLogical;
 	xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;
 
 	/* Header */
@@ -1370,9 +1373,10 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
 	XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);
 
 	/* array of TransactionIds */
-	if (xlrec.xcnt > 0)
+	if (xlrec.xcnt + xlrec.xcnt_repack > 0)
 		XLogRegisterData(CurrRunningXacts->xids,
-						 (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));
+						 (xlrec.xcnt + xlrec.xcnt_repack + xlrec.subxcnt) *
+						 sizeof(TransactionId));
 
 	recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);
 
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 629ac3a7d3e..1730b07810f 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD11D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 1dad125706e..c6693b93a65 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -69,10 +69,11 @@ struct XidCache
 #define		PROC_AFFECTS_ALL_HORIZONS	0x20	/* this proc's xmin must be
 												 * included in vacuum horizons
 												 * in all databases */
+#define		PROC_IN_REPACK				0x40	/* currently REPACK (CONCURRENTLY) */
 
 /* flags reset at EOXact */
 #define		PROC_VACUUM_STATE_MASK \
-	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
+	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | PROC_IN_REPACK)
 
 /*
  * Xmin-related flags. Make sure any flags that affect how the process' Xmin
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..9e6e7b18786 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -127,10 +127,13 @@ typedef enum
 typedef struct RunningTransactionsData
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK
+								 * (CONCURRENTLY). */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	subxids_array_status subxid_status;
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId oldestDatabaseRunningXid; /* same as above, but within the
 											 * current database */
 	TransactionId latestCompletedXid;	/* so we can set xmax */
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..edad609fa9a 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -47,10 +47,12 @@ typedef struct xl_standby_locks
 typedef struct xl_running_xacts
 {
 	int			xcnt;			/* # of xact ids in xids[] */
+	int			xcnt_repack;	/* # of xacts running REPACK (CONCURRENTLY) */
 	int			subxcnt;		/* # of subxact ids in xids[] */
 	bool		subxid_overflow;	/* snapshot overflowed, subxids missing */
 	TransactionId nextXid;		/* xid from TransamVariables->nextXid */
 	TransactionId oldestRunningXid; /* *not* oldestXmin */
+	TransactionId oldestRunningXidLogical;
 	TransactionId latestCompletedXid;	/* so we can set xmax */
 
 	TransactionId xids[FLEXIBLE_ARRAY_MEMBER];
-- 
2.47.3


--gwom7bl7ogtszo4k--





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